Want to add Horn to bass amp

[Natman]

Hi guys, I own a 2x10 Fender Rumble 350 combo which comes with a piezo tweeter (can be disabled with a switch).

The tweeter is pretty lame, it mostly introduces hiss that you normally can't hear and my Eminence BP102 woofers don't produce much highs (pronounced drop off around 2 kHz).

Anyway I'd like to add some much needed treble into the mix by replacing the tweeter with something respectable using a crossover if needed.

The caveat is I've never done this before. I've messed around with plenty of guitar speakers, but this is new to me and even though I have read stuff online, I'm not confident enough how to approach this. I do know the ohms and power rating need to be right or I can blow something easily.

Thanks for your advice!

[Jazz P Bass]

I would not recommend it.

This amp has an undocumented Class D amplifier in it.
It is designed (?) to run 2 10" speakers.

Adding an actual tweeter in parallel will change the output load.
As the power amp is not documented, who can tell what it's power rating is?
Plus you will need a crossover.

[Natman]

I would not recommend it.

This amp has an undocumented Class D amplifier in it.
It is designed (?) to run 2 10" speakers.

Adding an actual tweeter in parallel will change the output load.
As the power amp is not documented, who can tell what it's power rating is?
Plus you will need a crossover.

Thanks man, the Rumble amp schematics are available online and I have opened up 2 of them. The power unit is the typical Class D module by ICE Power. I can't verify all the details right now cuz I'm at work, but I have researched them in the past and found all the specs easily online.

Now it's possible I need a midrange driver and not a tweeter, but I want to get more clarity than the BP102's are giving me now (they work GREAT for lows).

[J M Fahey]

Here is the schematic (which improves outcome )
http://support.fender.com/schematics...atic_Rev-B.pdf
you can do it, but must solve a couple things first:
1) yes, it is a Piezo.
Which wouldn´t be so bad if it weren´t for the terrible match to woofers which have zero high mids,let alone treble, so you have a terrible hole in the middle.

2) you need a quite large horn, way larger than that piezo to reach down and meet the woofers, doubt you have space enough, would you consider adding a good 4" to 5" midrange speaker?

A PA type one, of course, it would need a crossover and a little "home" added to separate it from internal high pressure , nothing more complicated than a strong cardboard tube, properly glued and sealed and with closed back (a plywood disk or something).

Check USSpeaker and similar shops, the Faital Pro ones are killer and relatively inexpensive speakers, they have good magnets, some even Neodymium, but most important, aluminum wire voice coils.
You need something with generous output at 1800/2000 Hz and which can be crossed over at that frequency.

Those *heavy* coil 10" speakers have a built in series inductor even if you don´t add one, so their impedance goes up a lot above 1kHz.

[Natman]

2) you need a quite large horn, way larger than that piezo, would you consider adding a good 4" to 5" midrange speaker?

Yes definietely! I actually have a couple old fisher mid drivers in the basement that might work. They look like this:

A PA type one, of course, it would need a crossover and a little "home" added to separate it from internal high pressure , nothing more complicated than a strong cardboard tube, properly glued and sealed and with closed back (a plywood disk or something).

The current cab is vented at the bottom, I don't expect high pressure to be a problem?

Check USSpeaker and similar shops, the Faital Pro ones are killer and relatively inexpensive speakers, they have good magnets, some even Neodymium, but most important, aluminum wire voice coils.
You need something with generous output at 1800/2000 Hz and which can be crossed over at that frequency.

What would be considered generous output?

Those *heavy* coil 10" speakers have a built in series inductor even if you don´t add one, so their impedance goes up a lot above 1kHz.

Can you explain this a little more to me? I get that impdeance changes with frequency but don't grasp the implications.

Again, major thanks for helping me!

[J M Fahey]

Yes definietely! I actually have a couple old fisher mid drivers in the basement that might work.

I said PA type speakers
These old Alnico speakers will probably stand 5 to 10 W RMS by themselves (although they might come from a 40/50 W RMS Hi Fi cabinet) and die in the middle of your first Slap.
Check the Faital Pro midrange page at US Speakers:
Beyma - Faital Pro Speakers, Faital Pro Speaker Parts, Faital Pro bass speakers, Faital Pro speaker upgrades. Faital Pro woofers, crossovers, horns, drivers, etc. Faital Pro has some of the finest speaker parts.

Many of those will do, specially those specifically designed as such, not "small woofers"
You need a short light coil there, Bass already comes from the BP102.
The 3" and 4" ones might straight fit in your current Piezo hole, although they still need their own acoustically isolated sub enclosure.
Least efficient ones are 91 dB, not much ... but then Piezos are 92dB efficient so they are in the league.
When I said generous output I meant they can go way under 1800 Hz with no problem at all, while the piezo you already have drops like a brick under 3500 Hz or so.
Yes, it will have *some* output around 2000 Hz, but very constricted, distorted, and maybe 10dB down or worse, while the cone speaker will be coasting effortlessly
In any case, you will add a highpass filter (also sourced at US Speaker) set around 1800 Hz *and* a series protection lamp, 24V 20/25W is fine.

This speaker is KILLER at 99dB SPL Faital Pro M5N8-80 5" Speakers - Faital Pro M5N8-80 5" midrange speaker that has a lightweight neodymium magnet. Faital Pro M5N8-80 80 watt 5" high efficiency of 99dB SPL for all midrange applications. , stands 80W RMS by itself so it can be used with crossover but without need for a protection lamp (so your slap will tear heads, he he), but is too large to fit your cabinet, yet it deserves its own mini-cabinet, it can sit on top of the combo and be driven from external speaker out.
"Expensive" at U$118 but incredibly good, change won´t be ignored by the deafest one, he he.

This one again requires its own external mini enclosure, 95dB and U$44 . Faital Pro 6FE200 6.5" Speakers - Faital Pro 6FE200 mid-bass speaker. Faital Pro 6FE200 260 watt 6.5" woofer for all high quality mid-bass applications. Faital Pro 6Fe200

For reference, BP102 speakers are only 92 dB efficient ... and dull, which does not help to cut through.

The current cab is vented at the bottom, I don't expect high pressure to be a problem?

Oh, you do have high pressure waves inside, specially at lowest frequencies, which may even tear small cone apart; at least will push it away from the magnet and modulate midrange in a bad way.

What would be considered generous output?

compare this:

which is ultra cheap (U$24) Faital Pro 4FE35 4" Speakers - Faital Pro 4FE35 mid-high speaker has a wide frequency range from 90Hz to 20kHz and has a ferrite magnet - Faital Pro 4FE35 60 watt 3" has an efficiency of 91dB SPL for all high quality mid-high applications. which by the way is recommended for:

WORKS GREAT FOR UPPER BASS, MIDRANGE AND HIGHS IN BASS GUITAR CABINETS & 2 OR 3-WAY PA SPEAKER SYSTEMS
ALSO DESIGNED TO WORK IN LINE ARRAY SPEAKER SYSTEMS IN RISERS

to what you have now:

Notice that output at 2 kHz can´t even be DRAWN on the graphic

Can you explain this a little more to me? I get that impdeance changes with frequency but don't grasp the implications.

As JPB noted, you can´t straight add a speaker in parallel without further ado, and what was not mentioned but implied is that a full crossover, which fully separates low and high frequencies so they are not in parallel and drop load impedance, must be quite expensive because the low frequency section must pass 350W of power to 10" woofers.

BUT in this case, specially where we don´t need Hi Fi, we can get away using just a cheap high pass filter section for the midrange/tweeter and NOT use a complementary section for woofers , because we are not too concerned about response flatness, just not going down in impedance ... and if so, we don´t need a heavy wire, expensive coil in series with woofers, their own impedance rises and at 2 kHz, I haven´t checked the BP102 impedance curve but wouldn´t surprised at each of them having between 12 and 16 ohms above 2 kHz or so.

So in practice using just the highpass section of an inexpensive crossover coupled to the midrange should be fine.

By the way, thousands of cheap cabinets all over the place send woofers straight to connector and just add a plain capacitor in series with tweeter ... and nobody´s the wiser

[olddawg]

Check out the MCM Electronics Catalogue: MCM Electronics: Home and Pro Audio/Video, Security and Test Equipment
You can just use a bipolar cap as a hi pass filter to whatever you stick in it. I would use a piezo as it was designed. I usually put a 2uf cap in the positive lead. That works for most horns or tweeters. You can add a resistor or a pot if it's too bright. The impedance in parallel with the speaker load is inconsequential.

[Jazz P Bass]

How much 'tweet' do you need on a bass guitar?
(can you say "string squeak?")

A piezo should do fine.

Maybe the one that is in it is shot.

[vintagekiki]

http://support.fender.com/schematics/bass_amplifiers/Bassman_115_410H_schematic.pdf
Bassman® 115 / 410 Enclosures Schematic

http://elektrotanya.com/fender_speaker_crossover_sch.pdf/download.html

http://elektrotanya.com/fender_pa_horn_crossover.pdf/download.html

http://support.fender.com/schematics/bass_amplifiers/Rumble_350_2010_schematic_Rev-B.pdf
Schematics crossover is to positions B8

http://music-electronics-forum.com/attachments/32534d1421880316-documents-export-2015-01-21.zip
Schematics crossover is on page 2 (right)


Maximum operating voltage (one) piezo horn (tweeter) is 25 V~ and supports the power amplifier
4 ohms = 156W max
8 ohms = 78W max

For higher power amplifier is necessary piezo horn connect in serial
Two piezo horn connected in series can be connected to an amplifier that gives max 50V~ and supports the power amplifier
4 ohms = 625W max
8 ohms = 312W max

Piezo horn must be connected to the power amplifier via a 6dB crossover which is dimensioned for the appropriate voltage.

In practice, it is sufficient bipolar capacitor 4.7 uF operating voltage 100-150 V

For maximum protection amplifier and crossover in series with the crossover can be set bulb 12V adequate power.

vk

[olddawg]

http://support.fender.com/schematics/bass_amplifiers/Bassman_115_410H_schematic.pdf
Bassman® 115 / 410 Enclosures Schematic

http://elektrotanya.com/fender_speaker_crossover_sch.pdf/download.html

http://elektrotanya.com/fender_pa_horn_crossover.pdf/download.html

http://support.fender.com/schematics/bass_amplifiers/Rumble_350_2010_schematic_Rev-B.pdf
Schematics crossover is to positions B8

http://music-electronics-forum.com/attachments/32534d1421880316-documents-export-2015-01-21.zip
Schematics crossover is on page 2 (right)


Maximum operating voltage (one) piezo horn (tweeter) is 25 V~ and supports the power amplifier
4 ohms = 156W max
8 ohms = 78W max

For higher power amplifier is necessary piezo horn connect in serial
Two piezo horn connected in series can be connected to an amplifier that gives max 50V~ and supports the power amplifier
4 ohms = 625W max
8 ohms = 312W max

Piezo horn must be connected to the power amplifier via a 6dB crossover which is dimensioned for the appropriate voltage.

In practice, it is sufficient bipolar capacitor 4.7 uF operating voltage 100-150 V

For maximum protection amplifier and crossover in series with the crossover can be set bulb 12V adequate power.

vk

Yeah.. The old rule of thumb is 4.7 - 2.2uf to a horn or tweeter depending on how low the it will reproduce without damage. 22uf to a midrange driver.

[J M Fahey]

I would use a piezo as it was designed. I usually put a 2uf cap in the positive lead.

A 2uF cap in series with a Piezo does nothing, since the Piezo is a .15 to .3uF cap itself.
No RC filter effect when there is no R involved.

How much 'tweet' do you need on a bass guitar?
(can you say "string squeak?")
A piezo should do fine.
Maybe the one that is in it is shot.

If we talk string squeak we agree.
But OP is complaining about getting only hiss (and maybe squeak) through his Piezo, but not "music"
With which I agree, his 10" are dark muddy and no Piezo will help with that, he needs to cover the top octave which now he´s missing, nowadays he has a *hole* around 2000 Hz which no Piezo can cover.

There are some hybrid "mid horn drivers" (including a piezo disk and a coil) but those require a horn he has no space to fit in that cabinet, so next best is a 3" or 4" midrange driver.

Recheck the frequency curves and mentally superimpose them, my poor Photoshop skills do not allow me to do that myself.
To make it easier, I marked the 90 dB level and the critical 2kHz frequency which Eminence reaches only diving like a bomber shot down in flames:

Eminence BP102:


Fender furnished generic Piezo:

Notice that if you superimpose both curves you have a huge HOLE, smack in the middle of where metallic overtones from fresh roundwound strings live, we are talking played note harmonics here, not string squeak which is not " a musical note".

Now the FAITAL PRO midrange speaker, superimpose its response to the right of 2 kHz with that of Eminence BP102 to the left of 2 kHz.
Perfect flat smooth wide range response:


In fact the improvement is way better: the Eminence frequency response is 1 meter away and on axis; at 45 degrees, where most people will listen to it, including the Bass player (it´s a small combo sitting on the floor) , BP102 response is WAY down at such frequencies , easily 10dB down, in fact they do not even print the 45 degree curve, while small diameter FAITAL PRO midrange has incredible dispersion, look how little it loses even off axis.

[oc disorder]

Everything we have always wanted to know about Piezo's and Pizzeria's ! (made that last bit up!) Perhaps should be a PDF somewhere.....? (Vintage K ,Nick B ?)

Pulsar Developments Ltd - Piezo Tweeter Application Note

Hmmm got curious re where the (I thought defunct Motorola/CTS) piezos come from these days

"Piezo Source acquired the entire manufacturing line from Motorola/CTS, including the molds for the speaker housings. Our products are manufactured and tested on the original manufacturing equipment, ensuring that many of our products are 100% equivalent to the original Motorola/CTS piezoelectric speakers and receivers. "

PiezoSource Piezoelectric Speakers

The core products sold by Piezo Source are the original piezoelectric speakers and receivers designed, patented, and manufactured by Motorola/CTS for over 30 years.In addition to offering many of the original Motorola/CTS products, Piezo Source has developed new designs and materials to support the needs of new and existing customers and their developing applications. Our products consist of 62% Horn Tweeters, 13% Horn Drivers, 8% Voice Range Speakers and 17% Alarms.

Piezo Source, Inc. has been manufacturing and supplying these original horns since acquiring the exclusive rights, designs, and manufacturing line from Motorola/CTS in 2005. The diaphragm behind Piezo Source's original, KSN1001A, KSN1005A, KSN1056A, KSN1016A and the KSN1016B are at the heart of many manufacturers speaker and tweeters including:

COMMUNITY PZT2R Piezo
COMMUNITY CSX57 CSX57-S2 CSX57S2 CSX-57-S2 CSX 57
COMMUNITY CSX58 CSX58-S2 CSX58S2
CSX-58-S2 CSX 58
FENDER 1110A, 1110-A FENDER 110-ELC, 110ELC, 110 ELC.
FENDER 115-ELC, 115ELC, 115 ELC, FENDER 1205, FENDER 1205A, 1205-A.
GEMINI GT-3002, GT3002, GT 3002.
PEAVEY 112HS, 112, 112-HS, PEAVEY 122TC, 122, 122-TC,
PEAVEY 115H, 115, 115-H, PEAVEY 115HC, 115-HC, 115H-C
PEAVEY 115HS, 115-HS, 115H-S, SUNN 1205,
SUNN 1205A, 1205-A, SUNN 1275, SUNN 1275A, 1275-A.


EDIT: Here's the specs for the original CTS range and reduced PDF version of the CTS info in case its of any use.
and...olddawg "It was suggested to start putting a 2.2 uf cap in series on the positive terminal by a Motorola Rep."

[olddawg]

A 2uF cap in series with a Piezo does nothing, since the Piezo is a .15 to .3uF cap itself.
No RC filter effect when there is no R involved.

I've been told that a lot Juan, that because of the physics of a piezo it doesn't need a hi pass filter. However.... in practice, I found out years ago that in a lot of cheap or home made monitors using a Motorola piezo horn, they had a tendency to open up a lot when driven. It was suggested to start putting a 2.2 uf cap in series on the positive terminal by a Motorola Rep. I don't know exactly why it works. But they do seem to be more robust with cap. I always assumed it had something to do with the energy of the low frequency slamming the element without the cap?

[vintagekiki]

By itself piezo horn can play high power at frequencies above 2 kHz. (25V / 8 Ohm = 78W)
In distribution of the sound spectrum (above 2kHz) it is a great power, if one considers that the reproduction of high frequencies participates with about 10% power.

Piezo horn "not killing" power of the amplifier, piezo horn "kills" ~ Voltage at which it is connected, or ~ voltage low frequencies which usually declares rated power amplifier.
To piezo horn unloaded from unnecessary voltage low frequencies that otherwise does not play, but also protect it from permanent damage, it is desirable to use a crossover.

The principle of power over 100W should use two piezo horn connected in series, 6dB crossover and 12V bulb appropriate value (for f > 2 kHz = 50V / 8 Ohm or 312W)
In order to get "bigger" dB at frequencies above 2 kHz, can be used a larger number of piezo horn connected in parallel.

vk

[km6xz]

Adding the cap is a good idea on a system where the LF voltage swing is as high as on a bass amp. Piezo tweeters are cool devices but you do not want to bias them with a high voltage, with the lower fundamentals of bass looking like DC relative to the tweeter's effective output. So adding the cap is a good practical idea. Having some low level HF output from a bass rig can add space and presence in a live venue but it is very directional and a little goes a long ways. Often all that is reproduced by the tweeter is noise and ugly distortion products in a solid-state amp as it clips, unless slapping in which case, at levels below clipping the slap leading waveform it reproduced. It is just for the attack but not for power of the mids in slap, so the output usually has little information related to the harmonics of the notes.
I like Juan's solution provided the OP wants to change the sound of the whole rig. The current horn only reproduces the leading attack of a slap but little in the harmonic series of any of the notes so filling in the mids really changes the overall sound. Adding mid range will change the rig's tone signature a lot by providing a lot more low level harmonically related information. The mid range that is currently not heard is where the note character sits, and notes will become more distinct from each other. For many styles that is a great improvement in apparent dynamics and for full note voicing. In the studio, when players wanted to use their normal rigs, I had an outboard wooden midrange horn with crossover that could be set on top of the cab that filled in the harmonics in the 2-6khz range. It recorded a lot better and percussive sounds had a lot more note harmonic content that helps unmuddy typical live bass rig. We wanted individual notes to be well defined so the whole bass line could site at a lower level in the mix so keeping the vocals cleaner and lead guitar parts crisper. By playing lower, but the notes heard better, everything just got better for the recording. Paradoxically, adding mids and highs (which only have about 5% of the acoustic energy) makes the deep bass sound louder. They do not measure louder but our brains evaluate apparent power by the harmonic series from the fundamental. Ever notice how only 50s and 60s songs had strong bass notes in the song...but there was almost no power in the fundamental. 45s runtime length and broadcast regulations made sure there was no deep bass or kick drum fundamentals at all getting to the listeners ears. You heard the bass stand out, yet if you measured the note fundamental you would barely find it on a spectrum analyzer. That is because the brain fills in missing sensation or perception of missing sounds if the upper harmonics are present because those harmonics could only have been produced by a fundamental, heard or not heard. You hear a sound bouncing off a wall because the source is not seen but your head immediately turned to the "calculated" source of where it must have come from in order to bounce off the wall. A machine or microphone does not perceive and process sound the way humans do. The same concept, hear a harmonic sequence and the brain tells you of the presence of the fundamental. You are not at all confused what the fundamental would have been so you do not really notice that the radio station or 6X9 oval car speaker or car radio had no energy below 300hz. You had no problem hooking up with a kick drum in old rock and rock and found it easy to dance do because of that beat yet is was missing from the 45s or the American Bandstand broadcast and the 5 in speaker in the TV set. For the same reason, give the brain more harmonic perception and the inferred fundamental seems louder. This rig with a mid range handing 1-2 watts of signal will give the brain enough "data" to assume a much stronger deep bass power, more, by far, than the 1-2 extra watts of midrange energy. Everything will change by adding that simple insignificant mid and upper mids additional power.
With a decent wide dispersion mid you will hear the character of the bass itself more distinctly and you will realize you do not change strings often enough. If you have a shitty bass, or like to keep your "lucky" strings on for a year at a time, don't do this mod. You will definitely hear when the strings go flat. A simple 3 db/oct highpass filter works with Piezo but with a mid dynamic driver a 6-12db/octave would be needed.